1. Field of the Invention
The present invention relates to a gate valve and more particularly to a gate valve for use in a processing device for processing a semiconductor wafer or the like.
2. Description of the Prior Art
In a processing device for processing a semiconductor wafer, a liquid crystal substrate or the like, the wafer or the substrate is inserted into or taken out from one of many kinds of processing rooms through passages each having a gate valve. It is necessary to prevent as much as possible foreign matters from entering into the processing room.
Such gate valve is described in the Japanese Patent Laid-Open No. 156781/83. In such gate valve, a valve disc is moved up and down while separating from a valve seat, and the valve disc is brought into contact with the valve seat by urging the side surface of the valve disc toward the valve seat when the valve disc is positioned to face to the valve seat.
In said gate valve heretofore in use, a valve rod for supporting the valve disc and a valve housing are connected by a cylindrical bellows which is extensible, contractible and inclinable in order to cut off the vacuum space in the valve housing from the atmosphere outside of the housing.
However, a large pressure difference is generated between the outside and inside of the cylindrical bellows in the conventional gate valve, and accordingly, when the cylindrical bellows are curved according to the inclination of the valve rod for driving the valve disc an abnormal stress is applied on each portion of the cylindrical bellows, so that the service life of the cylindrical bellows becomes short.
The inventor found out by experiments that the above defect could be obviated by arranging the cylindrical bellows so as to project from the valve housing outwardly so that the outer surface of the cylindrical bellows is subjected to the atmosphere and arranging a pivotal point of the valve rod at a center of the axial length of the cylindrical bellows in the compressed state.
The present invention can be obtained by the above results of the experiments.